How To cut your coax to nulls or coax tuning

[@fourfortyroadrunner6701]

OK, OK, OHH KAY !!!! THERE IS NO REASON to "cut coax to nulls" or to a specific length when using coax as a feedline!!! The CORRECT LENGTH for a coax feedline is THE LENGTH THAT IT TAKES TO GET FROM THE TRANSMITTER TO THE ANTENNA!!!!

[@Travis141123]

Another ring in the CB radio SWR circus. If trimming coax is needed to adjust SWR, there is something seriously wrong in your station, be it a splatter-box amp or dirty transmitter. Similar to cutting your garden hose to get more flow...

[@izzzzzz6]

If the radio sees not only the antenna but also a combination of antenna mast and feed line, and this is the reality then it's a waste of time tuning the antenna while taking SWR measurements at the radio end of the coax and to be honest very few people tune their antenna at the feed point while at height. This is why it's important to tune when tuning a mono band vertical or unbalanced antenna at a midpoint frequency on that band. To prove this (and the effect is different on different designs of monoband antennas) There are many things you can try. Tune at the feedpoint then check the tuning at the shack. Add or subtract lengths of coax to a tuned vertical and see the difference. And regarding masts we enter a whole new world. Try an antenna on a glass fibre mast then put it on a metal one. The tune will change. You can get in the ball park with any length but you might be tuning your coax as part of the antenna system. Just as the mast can contribute as an unwanted radial so can the coax. I believe this is good practice although not crucial with most mono band antenna. After all Ideally I want all of the power to leave from the antenna and none to be reflected. This is why I want to see the tune of the antenna itself and not a combination of stuff like random counterpoise effects from coax and masts when tuning. The mast length and how it effects tune is a whole other topic as it's not only the height above ground and distance from other objects buy it will on many antenna try to act as a counterpoise and a mast can be any length. So many variables that myths emerge, different frequencies, unbalances vs balanced systems, transformers, ground laid radials vs radials in the air. proximity to objects. The idea is to control as many of the variables as possible as there are almost always compromises in amateur radio installations. This puts the argument back on track. Some vertical (and some other) antenna can tune very differently to each other when each compared on 2 different lengths of coax. If the coax can be made to look virtually invisible at the desired frequency that you will be centring the tune of the antenna around then we can be more sure that we have tuned only the antenna from the radio end and not a combination of antenna and feed-line. I would like to draw also some attention to the general lack of people talking about how the metal masts also become part of their antenna systems to some extent and why are people not fine tuning their masts when they are electrically connected? Yes it should not really be an electrical consideration yet it all too often makes a large difference to an antennas tune. Put the same antenna on a different mast and re-tune it!

[@Pioneer936]

@@izzzzzz6 correct it's an antenna system

[@wesleycardone2245]

Yes, you can cut a feed line to resonance. But the SWR remains unchanged. Map it out on the Smith Chart to verify. The author in this video is suggesting that achieving resonance via the feed line is equivalent to a unity SWR. In an experiment there might be some SWR movement due to a flawed test procedure or parasitics, but in theory, the length of a feedline is irrelevant for changing the amount of reflected wave.

[@izzzzzz6]

did you include the metal mast on the smith chart? Real world does not always act exactly like the mathematical ideal

[@ChrisRobinsonKF6NFW]

most dont understand that the only place to take proper SWR measurement is at the antenna feedpoint, otherwise they are trying to tune the coax as well. Otherwise the coax is simply an extension of the radio and nothing else. As well, most dont understand the relationship between RF Power, Freq, Line Loss or even the choice of coax and line loss associated with that, such as the differences between RG58 , RG 8 and LMR 400. RG 58 may show a perfect swr, however install a better coax and suddenly it may show a high swr. and the truth is it was a High swr all along , but the line loss was great enough that it fooled the SWR meter into thinking it was perfect. The SWR meter is just a dumb meter!

[@Pioneer936]

@@wesleycardone2245 can be good for impedance matching

[@Pioneer936]

@ChrisRobinsonKF6NFW the best place to measure the mismatch is at the antenna that's correct but measurement of the resulting swr on the line is the measurement at that point ,to understand this better if an analyser was used you can see the difference in impedance at different points along the length of the feedline

[@jeffreymiller36ny32]

Wow your in NY. ME TOO I do similar I made a small dummy load on a T. and plug the coax into one side to show it has no reaction. Great job. Simplicity is everything for people. Thank yo

[@12NYDarton]

I'm in Watkins Glen NY 🤘 #12...

[@dannelson8556]

wait are you actually using 1/4 waves stubs to interconnect components so the coax is "invisible" to the connected devices LOL Oh you must be a CB tech LOL As a retired electronics engineer, this is nothing but a bunch of male bovine excrement. Don't get me wrong Coax stubs are very useful in making things like phasing lines or precision phase corrected lab jumpers, But it's useless for interconnecting things like antennas and amplifiers to your radio. This is a prefect example of an old CB wives tail, some CB fool read in a ham radio book that a 1/2 wave stub will present the same impendences at the load as it does at the source and that it meant that the coax should always be cut to the nulls LOL Damn our school systems are failing us.

[@feeatlastfeeatlast5283]

Typical. Look at the "great video" and "thanks, just what I needed" responses. Grit my teeth.

[@bill-2018]

I know, wives tale. I'd need a 44 foot trimmed jumper lead for our 60m band, it is by chance about 50 feet but I didn't precisely trim it like this shows, and 550 feet for our 2200m band! Trim the aerial not the coax. Why do they think things change up to the SWR meter? Why don't they tune the whole system, jumper, SWR meter and coax by adjusting the aerial if it bothers them? G4GHB. Actually it's not 550 feet, that's metres, it's more like 1700 feet!

[@feeatlastfeeatlast5283]

@@bill-2018 Answer, because they don't understand electronics theory. Actually, hardly any hams do. They take a tiny (probably, that a half wavelength of coax repeats the Z) fact and distort it out of proportion! The sad part is whenever you see one of these and you check the responses then you see how ill informed and gullible the viewers are. One of my favorites, Fine Tune CB - he gets people to pay him good money to "Tune" a brand new radio, as if the factory didn't know how to do it.

[@bill-2018]

@@feeatlastfeeatlast5283 Can't be bad charging people money for something already working. I think I've seen a couple of his videos. They are obsessed with trimming jumper cables as if that cable before the SWR meter is a problem and no problem beyond it. 73, G4GHB.

[@dannelson8556]

exactly, coax length does not tune the antenna system It only changes the z seen by the transmitter. If you're antenna is resonant then coax length isn't going to change that. this is just a perfect example of illiterate people reading something in a book and distorting it.

[@MrMotorchild]

So... a different length of coax is needed for each band??? Example: someone working the 10m band will have to use a different length of coax to work the 40m band???

[@jacuswoczega9180]

Good question. This is fundamental error in "coax tuning"

[@jacuswoczega9180]

Or on different parts of band. Many ham bands are wide 7-9% of central frequency, which gives HUGE difference on phase.

[@bill-2018]

Indeed. I have two dipoles (10m and 15m) on one coax and three (20m, 17m and 12m) on the other. Both coax lengths about 25 feet so probably both wrong by his reckoning. Why do my aerials work? What length would he say I should be using for my 4 element 2m collinear? G4GHB.

[@ChrisRobinsonKF6NFW]

I have heard this myth for years and am still amazed people believe this! I have never heard of making your coax invisible in your system. Someone care to explain. In all my radio setups, I have always setup with the length to go from radio to antenna, and tuned the antenna for best resonance, lowest vswr. Put a 1:1 choke on as needed for CMC depending on antenna design. Cutting coax to a specific length to accommodate the antenna besides connecting it, that tells me your antenna is the problem, NOT the coaxial cable. Some exceptions do exist, but are very antenna specific. it is not a blanket rule. There are books and educated folks to help with this. Some of us are also RF engineers!

[@fnordist]

I always utilize ferrite beads, typically around 15 pieces, to achieve an impedance of about 150-200 ohms at the operating frequency, equivalent to approximately 2-3 kohms. This is crucial because RF currents distort antenna matching, etc., and I prefer to avoid RF interference in my car. Inside my vehicle, I've inserted the ferrite bead choke balun into a brass tube and fastened it to the roof. While it might sound excessive, it's also to address vibrations and mechanically relieve strain on the coaxial cable. After all, it's nearly 500g in mass, and the brass aids in cooling the ferrite cores.

[@izzzzzz6]

It's similar to not wanting your mast to become part of your antenna system. If the antenna is designed correctly it should be able to work on an insulated mast, you will find the swr changes greatly on say vertical antenna depending if you mount them on a metal mast or a glass fibre mast. No who talks about tuning their masts, we talk about height above ground but we don't talk about fine tuning metal mast length or really expect them to be part of the antenna system yet they are. same with coax. it's not supposed to but it does. You don't have to cut it, you can try with a balun or add lengths when you patch together the other gear in the shack. I find I get different results with different lengths of coax regarding antenna tune. If this is the reality then it's a waste of time tuning the antenna while taking SWR measurements at the radio end of the coax (unless the coax is invisible) and to be honest very few people tune their antenna at the feed point while at height. This puts the argument back on track. Some vertical (and some other) antenna can tune very differently to each other when each compared on 2 different lengths of coax. If the coax can be made to look virtually invisible at the desired frequency that you will be centring the tune of the antenna around then we can be more sure that we have tuned only the antenna from the radio end and not a combination of antenna and feed-line. I would like to draw also some attention to the general lack of people talking about how the metal masts also become part of their antenna systems to some extent and why are people not fine tuning their masts when they are electrically connected? Yes it should not really be an electrical consideration yet it all too often makes a large difference to an antennas tune. Put the same antenna on a different mast and re-tune it! If the coax starts to become part of a radial in the system it's not ideal and it makes tuning the antenna from the shack potentially inaccurate. Now, multi-band antenna is a whole different story of compromises and tricks.

[@ChrisRobinsonKF6NFW]

@@izzzzzz6 Malarkey! If you are placing your SWR meter anywhere other then the base of your antenna when measuring, you are not checking for proper antenna tuning. The only way to properly tune an antenna, and the only place it matters is at the feed point of the antenna. There is no other place in the system that impedance matching that it matters. If you are using a 50 ohm line then the only place it matters is at the antenna. The radio is 50 ohms, period, the coax is just an extension of the radio connection to the antenna. the antenna is the only place you need worry about the impedance mismatch. The antenna may have a fixed impedance such as many verticals, or tunable. If its a fixed then you will need to do some tricks to match it, such as a transformer method, also called a balun. If your baluns are getting hot, there is a problem such as a mismatch, and you are. that heating effect is called the curie effect. You need to avoid this at all costs. as curie is approached, the effectiveness decreases. Eventually you may crack or melt your balun. As for the antenna impedance, you are only able to match it, or accept the mismatch, which will cause a high swr. No amount of cutting coax will change this. Your SWR meter is a dumb device. if moving the SWR meter to different points in the coax shows you different readings there could be a couple things happening. You could have found a voltage minimum for the frequency to which you are testing, which will look like a good match. Or you could have some Common mode Current on the outside of the shield causing you an issue. Again a dumb SWR meter doesnt know where it is in the system, it just sees what your putting in and it sees in return. It may also be seeing a high loss in the coax due to bad choice of coax such as RG58 which has a high loss, in which case it again fools you into thinking you have a perfect SWR, in truth you have lost so much power that the reflected power is so low that the meter just isnt seeing it, thus a great reading. Again, its a dumb meter. Most folks do not understand SWR vs Freq, vs coax length and RF Power relationships. More folks need to take time to read the books and do some real testing at the antenna, and no where else. if you are testing anywhere else, you are not testing your antenna properly, you are testing your coax as part of the antenna, and that is a miscalculation.

[@izzzzzz6]

@@ChrisRobinsonKF6NFW Not many amateur or CB operators do this. In the real world many people are aware that the antenna tunes differently at height. I specifically was looking for a VNA with Bluetooth connectivity to be able to measure the antenna at height. How many people do you see tuning at height? What ? With an antenna analyser and a go pro up the mast so they can than look at the data later? Might as well pull the mast up and down 10 times making micro adjustments which is what you are saying is pointless. Because any other way you must be taking the SWR measurements down some length of feed-line. Now we also know that we can calibrate the VNA from the shack end of the coax by putting the calibration resistors open and closed adapters at the feedpoint end, thus making the coax invisible to the VNA. This is the way to do it but then ask yourself why after tuning and connecting back to a SWR meter or radio the tune has changed again. Then we can add or subtract lengths of coax and it continues to change. So in my opinion. yes. 1st tune at the feed-point. But with unbalanced mono band antenna and some multi-band antenna you are going to see a false reading as such. But it's not really a false reading it is still telling you that even though your antenna is tuned correctly something to do with the feed line is now reflecting power to the radio thus potentially trapping it bouncing around the feed line or reflecting into the radio or amplifier. Just tune it for mono band work then everything is happy. If it was not true then i would see no change with different lengths of coax and I can say that some designs of antenna do amplify the effect more than others depending on how much capacitance and inductance they use. Now lets talk about electrically tuning mast length and how masts and other surrounding objects want to act as part of the electrical system.

[@bill-2018]

Tune the aerial not the coax. I tried to buy invisible coax but couldn't see any. Why do any of my aerials work with random lengths of coax? Because it doesn't matter. C.B. radios must be badly designed if coax length makes this difference he is showing us. G4GHB.

[@Metalhead396]

Making a half wave is totally different than a quarter wave. You need a tee and a dummy load on the MFJ.

[@electromechanicalstuff2602]

That's how I do it. T with small direct dummy

[@glasslinger]

OMG, the schools (or lack of!) are failing!

[@electromechanicalstuff2602]

Ya cause he made it real simple and u still don't understand simple science

[@bill-2018]

@@electromechanicalstuff2602 Put a VNA on any length of coax with a 50 Ω dummy load on the end and look at the frequency response. Virtually flat from 1.8 MHz to 29 MHz at the frequencie I set it for. There is no 'magical' length of coax to use. G4GHB.

[@5BASSIP]

The UK is still feet and inches. The kids are being into meters etc. most adult radio guys are still talking feet and inches. GL 73.

[@Warner-uf3mf]

I remember someone telling me many years ago, in multiples of 14 feet, I was just getting into cb radio back then, one guy said length didn't matter, but I cut my coax to what your showing and apparently it does matter. Thank you so much for this video, I had forgotten alot since I was a kid.

[@feeatlastfeeatlast5283]

Whoever told you that had no idea what he was talking about. But instead of investigating and learning you ate it up. Hopefully you no longer do that. Info is available, books still are available.

[@bill-2018]

Put a 50 Ω dummy load on your coax and see what your power is. Try another length of coax. Is there a difference? 6 inches or 20 feet should make no difference unless it's very lossy coax. Why do you believe in a magical ¼λ coax? G4GHB.

[@bill-2018]

You say it matters. How did it change things? I've never cut coax to a specific length. I'd need 44 feet on my 5.262 MHz inverted vee. I haven't. G4GHB.

[@waffleone3]

Using 468/freq. To find half wave in free space will get you close. But this is formula for a half wave dipole, which is about 5 % shorter than free space length, due to end effect of the wire. Best to use 492/freq. to get half wave length in free space then apply the velocity factor of coax you are using for a more accurate number.

[@radioguy19510]

There is no reason to cut a coax cable to a quarter wave (or other specific length) for jumper cables. you can use any practical length to connect your radio to whatever you need to connect it to. I f for example your Watt meter is only 2' away from your radio, you can't need a 6' piece of cable (it isn't going to affect the performance of your radio in any way). Making a coax cable any longer than you need is just a waste of coax!

[@ChrisRobinsonKF6NFW]

we can argue that the excess cable is a loss of signal, but certainly not a gain in invisibility to the system! Even if only the difference of 4 feet. imagine if we are working at V/UHF freqs, and each foot adds up with loss. I worry more about the connectors chosen and lets get rid of every extra foot of cable in the system that we dont need. the only extra footage MIGHT be the drip loops and room to move gear but past that its all BS. You are absolutely correct!

[@jacuswoczega9180]

​@@ChrisRobinsonKF6NFWYou speak about different thing

[@ChrisRobinsonKF6NFW]

​@@jacuswoczega9180How so? Explain. I speak of the exact same. I may have explained differently and put into different context. However, extra coax is extra loss. Do not cut a cable any longer than you need it. There just is no need. It's pure waste of money and rf power. I am willing to explain and show the math and work though to anyone. I'm also willing to admit where I am mistaken if you show me that also

[@jacuswoczega9180]

@@ChrisRobinsonKF6NFW I agree. Only small clarification, most of thread is about magic length. Loses are generally known, and almost no controversial (one exception: microvawe low loss cables fof CB)

[@ChrisRobinsonKF6NFW]

@@jacuswoczega9180 but the point being, the magic length is whatever it takes to get from radio (point A) to antenna (point B) any length longer is a waste. If you wish to cut for some wavelengths to solve an antenna issue, this is clearly not the way to do it.

[@bill-2018]

Why? So the only problem occurs before the SWR meter and not beyond it? If you put a 50 Ω dummy load on a 10 foot length of coax and then add a another 10 foot, 20 foot or 30 foot it is still a 50 Ω load and still a 1:1 SWR. You don't adjust anything. Nothing changes and still a minimal r.f. loss. You put an aerial on and adjust the aerial for 50Ω, put a jumper lead of any length in and it should still be 50 Ω on a well matched aerial. Tune the aerial not the coax. It sounds to me if you have to cut jumper leads to length you have r.f. on the outer of your coax affecting things or the aerial is not a true 50Ω. I've never cut any to a specific length after years of making aerials. I'd need a jumper lead of around 44 feet (¼ λ) or 88 feet (½λ) for our 60m band and a ridiculous whopping 550 feet (¼λ) for our 2200m band. G4GHB.

[@richb.4374]

I was thinking the same thing. I've been into radio for 50 years and never once tuned coax on any antenna and was always able to obtain a flat match. If SWR is changing from length, that suggest common mode on the shield of the coax.

[@bill-2018]

@@richb.4374 It's as if they believe a 6 inch length or 20 foot length of coax won't produce 4 Watts unless it's the magical ¼λ. They just don't get it. A 50 Ω dummy load proves otherwise. 73, G4GHB.

[@bill-2018]

Actually it's not 550 feet, that would be 550 metres. It's even worse, about 1800 feet! G4GHB.

[@tonyfremont]

​@@richb.4374Most antennas aren't 50 Ohm perfect matches. By using 1/2 wave multiples, the radio will see the same impedance as the feed point, since that's what 1/2 wave sections do, repeat the impedance they see at the other end. This way, the matchbox matches to the feed point impedance and not some complex reactance that includes the feed line, and consequently it's length. If you do things this way, your antenna won't suddenly be out of match because you swapped a different patch cable in your shack. This is a real issue with VHF, your swr changes dramatically when you change patch cords around. Whenever your antenna isn't a perfect match to your feed line, your feed line becomes part of your antenna due to the swr. By using half wave multiples you nullify the effect as much as possible. The swr you measure in your shack truly represents your antenna situation by itself since it's impedance is seen at the radio end, not the complex conjugate. 1/4 wave stubs have their own special uses.

[@bill-2018]

@@richb.4374 49 years radio here and in the early days I did not have an SWR meter, I just tuned for maximum r.f. out. After building the resistive SWR meter it proved maximum r.f. out was minimum SWR. In fact I built it only about ten years ago and calibrated it four years later! G4GHB.

[@gordonlovett71]

Thanks for the simple explanation. Your method works great. I usually talk on some lower frequencies below 11m channel 1 so I implemented your advice when I made my next jumper but made it a little over 6' (6'-5") and it came out perfectly, in fact I was able to cover the entire 11m band up to 27.425 down below 26.865 and my SWR never went above 1:1.2. During my years in the radio game some have told me it doesn't matter and others have said differently but now I know it does. Thanks again, I'm off to make a few more jumpers.

[@ironhead320]

If you can use a nano vna what do you set it on

[@electromechanicalstuff2602]

SWR, impedance, usually all I use. U can actually see the sine waves and nulls in a vna. Put your curser at your frequency then start trimming till the null slides over to your frequency. Done

[@ironhead320]

@@electromechanicalstuff2602 ok thanks

[@ironhead320]

Did the math with RG8 comes out to 5.6 ft

[@jacuswoczega9180]

For me more important is not HOW cit, but WHY. 1. Impossible to "tune coax" to wider frq range. 2. Normal rezonant antena don't require coax tuning, only very rare or bad tuned antennas

[@bill-2018]

Do you think an SWR meter is somehow an isolator? One side of the SWR meter is not connected to the other? It's like a coax connector joining two cables together. The inner two are connected together and the braids are connected together as in one cable. In reality you have one length of coax with a meter placed conveniently near the transmitter. G4GHB.

[@Pioneer936]

@bill-2018 does the impedance at the radio change with various line lengths when there is a mismatch

[@bill-2018]

@@Pioneer936 73

[@rangertechdx3511]

When making phasing cables or stubs the correct constant is the free space in a vacuum which is 492 not 468!

[@dandypoint]

Absolutely correct! The 468 already includes a “ ball park” velocity factor. An electrical halfwave of coax is only significant if you need the exact antenna impedance to appear at the input of the coax. The quarter wavelength can be used as a transformer if there is any SWR on the line. For general use there is no point to use a specific length of coax. It certainly does not change the SWR on that coax. This does not make the coax invisible. Short lengths of coax have minimum loss anyway.

[@rangertechdx3511]

You can't tell this guy anything. He already knows it all. Just like he thinks you have to have a resonant antenna to have low SWR. Resonance and SWR aren't one in the same. You could have God only knows what impedance and still have a resonant antenna and you can have a perfectly good match and the antenna be no where near resonant.

[@dandypoint]

@@rangertechdx3511 I had heard someone mention there were videos like this out there but I did not believe anyone thought that until I saw this!

[@AB1Vampire]

There is merit to this. What about a multiband compromise say 10=-40 meters?

[@55weirdharold]

Thanks for the video. Exactly the information I was looking for. 73

[@troydavis2424]

Man unless you have a twin that sounds like you.,,back in the day did you build a suburban 2 tube (2) 3cx3000 ..the suburban was a old school and you had 2 sticks on top..Al Capone BYU got down...if not even tho I known this info ,Love the videos big bro keep up the good work...

[@Dark_Knight_USA]

Greetings: Yeah, everyone should have their own Mighty Fine Junk. Remember there is no load and Ur hand effects also Thx 4 the share.

[@N2YTA]

The 468/F in MHz allows for a 95% velocity factor.

[@Biastai]

Why did you apologise to the UK for using feet as a measurement? From Wikipedia: The foot ( pl. feet), standard symbol: ft, is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, ′, is commonly used to represent the foot. In both customary and imperial units, one foot comprises 12 inches, and one yard comprises three feet.

[@kurkradford479]

Great video if you want to make 1/4 or 1/2 wave elements for vertical arrays. Even easier than nanoVna. Remember to leave a little long for connector installation trimming. I try to measure the normal trimming of your PL259 solder connections and compensate for that as the last trim. Make a log of your trim lengths and how much it effected Freq. so you know what to make the last trim. K6RAD

[@K4DL-AL]

On the frequency I use every day my quarter wave jumper would be over 41 feet.

[@bill-2018]

Think how long on 472 kHz or even worse on 136 kHz. G4GHB.

[@fitcher-armchair-sleuth]

Just curious .. Years ago (mid 1980's) I talked a local guy who said he took like a 12 foot piece of rg-213 coax and kept chopping it down a few inches at a time until he got a good match between the his radio and amp. I asked him about the mismatch (very high swr) and he said - "It's the coax, it needs to be the correct length between the amp & radio, or they'll always be a extremely high swr." This was a cobra base cb radio, base boomerang 250 amp to a vertical 5/8th wave antenna. I don't know what length he ended up with, but said he got it. Is there some (sweet spot length) magic length between a radio and amp that needs be got right?

[@lilbump406]

This is the correct way to do a 1/4 wave length of coax. But when you do a half wavelength of coax you need to short the center conductor to the shield while you analyze the coax. Good video.

[@flyingdoctor99]

wow! Thank you for the instructions. Do you plan to provide some messurements with an antenna connected? I mean different length to the exact length with SWR comparision and the resulting RST by same QSO partners? That would be great.

[@Dallas-Rife-UDX-347-Tennessee]

This was a game changer on my station . Completely eliminate my reflect on my accurate meters (Bird) . Very good information .

[@NeedleBender785]

Great video, really appreciate the info!!

[@raymota4515]

How long do you want this cable? Only about a week. LOL.

[@arildoaparecidocosta5729]

Ótimo trabalho parabéns bazuka Foz do Iguaçu PR Brazil 🇧🇷🇧🇷

[@LeeWhiting-k3x]

Unless your RG-213 is using PTFE for a Dielectric, the V.F. isn't 69.5. If it is "normal" RG-213 and uses Nylon as a dielectric, it's V.F is 66%.

[@LeeWhiting-k3x]

Don't "solder" coax with a foam dielectric. Use a clamp or crimp style connector. If you solder the shield, you will melt the foam and the coax is no longer "50 ohms" by design.

[@VE9ASN]

Invisible coax lol, must be a cb thing.

[@jacuswoczega9180]

Yes, CB myth

[@Jon-zr5om]

Correct me if i'm wrong, but you cut length in odd multiples.

[@n3iyr]

This is a complete waste of time.

[@RA-II]

SWR should match with both the coax and antenna. Not just the coax

[@benjaminmeadows1380]

I allways asked cb tec that buid my coax cables for how long was best 6 ft was unless used steal whips antenna then little longer

[@boricuaengeorgia7332]

That makes a lotof sense but how about from amp to antena on Mobil

[@CharlesHood-fx7hy]

Thank you sir

[@vetinger]

THIS VIDEO IS FOR WIRE ANTENNA and IS NOT FOR COAX...or this is my mistake?

[@bill-2018]

He's making out that coax MUST be cut to a specific length for it to perform it's best. He seems to think his SWR meter is some kind of isolation device and there are two totally independent cables which are not connected together by the meter. If he measured coax at the transmitter end through to the aerial his magic carefully trimmed jumper lead and half wave to the aerial has gone. G4GHB.

[@robertbobbitt8448]

Why would you want the coax resonant? It then tends to radiate making the coax part of the antenna Coax resonance is a bad thing

[@Pioneer936]

Coax won't radiate because it's half wave ,coax radiates because of an antenna imbalance

[@bill-2018]

As a test and for a future video to disprove resonant coax must be used I made my coax resonant at 14.040 MHz. I have no problem with it when on 14 MHz. Ferrite rings stop r.f. on the outer braid so it's not part of the aerial, unless it is wanted say for a vertical in place of radials. If I add both jumpers of 45" and 20" it's resonant frequency goes down to 11.320 MHz proving the nonsense of tuned coax and 3', 6' 9' or whatever recommended length of jumper is B.S. That resonant length of coax has gone. I have to take my SWR meter out because it's a Wheatstone Bridge type and consumes half my power. It's great for tuning aerials because the tx never sees above a 2:1 SWR while adjusting them. G4GHB.

[@Pioneer936]

@bill-2018 your experiment does prove that the impedance changes with coax length and that by putting a different length of patch lead in can make the transmitter see an impedance it likes

[@bill-2018]

@@Pioneer936 Yes, on an open ended coax which is not the real case when 50 Ω is connected. It is an open ended half wave stub at only 14.040 MHz but flat right across 1.8 MHz to 29 MHz with 50 Ω connected. Don't take my word for it, try it yourself. I'm waiting for sunny weather to get good illumination in the bedroom before doing the video.

[@Pioneer936]

@bill-2018 most people don't have a 50ohms perfect match, this is probably where some misunderstanding arises

[@frankgeeraerts6243]

Thank you ....

[@M0RMY]

Why? Just why? This a waste of expensive coax and shows a real disregard for physics and RF engineering.

[@bill-2018]

He seems to think his SWR meter is some kind of isolation device and there's a 'transmitter side' and an 'aerial side' not connected as one cable by the meter. Look how many people take this useless advice. There must be something very wrong with C.B. radio design if it makes a difference. G4GHB.

[@cordaman176]

im in ny also. where in ny are you?

[@cik7897]

Solid & simple way of helping the average RTO make more reliable contacts.

[@popcorn913.]

Thank you

[@franciscolopez3229]

Sir, do you the same procedure for the coax from the antenna down to your shack? Thank you.

[@bill-2018]

Exactly. It's nonsense! I've never in 40+ years trimmed coax to any specific length. Tune the aerial not the coax. G4GHB.

[@bill-2018]

6 inches of coax or 20 feet of coax unless very lossy still produces 4 Watts. Try it on a 50 Ω dummy load in place of the aerial with different lengths of coax. Why do you believe in a magical ¼λ length of coax? The reason you might see a difference is R.F. on the outer of your coax. G4GHB.

[@fido3561]

Hey G4GHB!! Make a video and show us how it's nonsense. Share your knowledge G4GHB. KCU3589.

[@bill-2018]

@@fido3561 I'm thinking I will do a video showing it doesn't matter. I set things up yesterday for 24.94 MHz as my oscilloscope isn't good at 28 MHz, it's not made to go that high. First read 50 Ω at the tx: 50 Volts, then the same 50 Ω with the magical ½λ: 50 Volts, adding 39" of coax should throw it off, right? No, still 50 Volts. Add another 18½" and still no difference. Output test at the 50 Ω carbon resistor adjusted to read just on the red line of an r.f. pick up meter (meter, diode and capacitor), meter from a hi-fi or something. Meter and coax trapped on the desk so nothing moves. On the ½λ it's just at the red line, add 39" at the tx end so nothing is disturbed: no difference, add 18½" more and still no difference. The same power output sensed by the meter. C.B. theory says I should have a mismatch due to different coax lengths and less power at the end. I did use a ferrite ring so no r.f. gets on the outer of the coax as indeed it shouldn't anyway being a resistive load but to make sure I used one. If coax length makes a difference it means there is r.f. on the outer braid of the coax. The SWR meter can go anywhere too as I proved. Coiling coax had no effect. No figure 8 needed. Again if it does then ferrite rings are required. Just all things I have known for years. 73, G4GHB.

[@sirmister4411]

He has the cb brain oh boy this is so wrong and so many variables are not correct. He must have a cb backround

[@SureshKumar-nk2ok]

sir this is only for HF range .please suggest for UHF range too regards

[@electromechanicalstuff2602]

I prefer to make mine in half wave lengths. Use a dummy load on a t.

[@lanefireline9552]

I'm sure glad this wasn't a college course.

[@GroundControl204]

Great video, you just got a new subscriber. 73👋🏻

[@bill-2018]

I'm going to make a video to disprove that a half wave length of coax must be used. There is no 'magic' length to use as radio amateurs keep saying. Test 1. Simple proof with a multimeter, there is one continuous length of coax from tx to aerial. Test 2. Tx, oscilloscope and 50 Ω dummy load. My 'tuned' coax at 14.040 MHz tested and results as follows: Drops 1 Volt at 14.040 MHz. Drops 1 Volt at 10.1MHz. Drops 1 Volt at 18.1 MHz. If my coax is so mismatched how can I get these results? Should I get anything out at 10 MHz and 18 MHz from my untuned coax? My coax is resonant at 14.040 MHz then if I add my 45 inch jumper through the SWR meter the frequency goes down, if I add my other 20 inch jumper it goes down again to 11.320 MHz as measured on my VNA. As expected! The 'magic half wave' has gone. Don't just look at 27 MHz. There is no resonant length of coax to use. My VNA shows an almost flat line from 1.8 MHz to 29 MHz. My coax can be used anywhere within that range. Or will you say I just hit lucky with it? G4GHB.

[@Pioneer936]

@@bill-2018 look forward to seeing the analyser hooked up to different lengths

[@bill-2018]

@@Pioneer936 Why don't you try it yourself?

[@Pioneer936]

@@bill-2018 done that I know the outcome, it will show the impedance changes with different lengths when there's a mismatch

[@bill-2018]

@@Pioneer936 I have planned my video about the myth of 'tuned coax'. 'Tuned coax' is an open half wave coax stub. high impedance at that freq. and a short to others. Great, 'tuned coax' working, just as C.B.'ers say, Add an SWR meter and jumper lead and the frequency goes down, no longer 27 MHz. How and why does it still work at 27 MHz? It's now tuned to a lower freq. Put a 50 Ω dummy load or aerial on and check with your VNA. Look at the response! G4GHB.

[@Pioneer936]

@bill-2018 great ,,,when you do the video make sure you show the impedance changes with various lengths from a mismatch so people get an understanding of where the myths have developed

[@electromechanicalstuff2602]

Its so crazy its like the same 4 guys on every single cb or coax video crying in the comments about how ive been doing this 50 years and i dont know how to use a VNA to tune outputs i use 50 watts and have never had a problem with my set up. This is a waste of time...Bla bla bla. Its such a waste of time that they spend ALL of their time searching for these videos just to complain about them......

[@paulm0hpd319]

Just use an antenna tuner

[@paulwright7551]

If we tied your hands up, could you still talk?

[@deepwaterescue4u]

good information thanks for making this video..73s 007

[@Stevef-sk3jc]

nice and simple.. these self proclaimed engineers below.. are not likely real in the true sense.. this tuning.. is important in the uhf and above as when an antenna is made to 46ohm and the transmitter is 46 ohm and the coax is 51 ohm...or other variations and this is a true senario every thing being a true 50ohm dosnt always happen.. this 1/4 trick is nessassary.. also with long lengths of cable the velocity rating of the coax cant be used.. as this changes with frequency...this video and other methods should be used

[@PowderMill]

CENSORSHIP? My previous comment (part 1 of 2) was censored / deleted within 10 minutes of my posting it, so I’m guessing it was KZbin I was bestowing my thanks and gratitude for this video and sharing our method of terminating, etc… Other than a reference to the mentally challenged pederast who is currently an inhabitant of the White House, I don’t know how else I offended the Big-Tech Over,odds….?

[@12NYDarton]

Funny how operators dont believe this. Ha... Jokes on them. You run poweryour SWR's go up. Because your coax isn't tuned. Why tune everything else and not the most important thing. What are swr's.. Heat. Whats heat do to our equipment... Burns it up. My Dead key is 1000 bird. My pep is 4700. My swr's... X=0... my swr needle doesn't move. Why because I tuned my coax too. 50 ohms... So believe what you want and leave this stepout. #12- Watkins Glen NY waving

[@bill-2018]

You really think the jumper lead and the aerial lead don't connect through the SWR meter as one cable? They are entirely different cables? No coax of mine are tuned. Either 20" and 45" jumper lead depending where I place things, my dipoles and inverted vee use enough coax as necessary to get to the aerials. 2m collinear not carefully trimmed either but approximately 10'. What would he have me trim that to? ½λ which is about 19" before Vf taken into account? That wouldn't be very high up. How about ⅛λ, or ¼λ,⅜λ, ⅝λ,⅞λ or what? G4GHB.

[@12NYDarton]

​@@bill-2018 The proof is in the SWR.

[@bill-2018]

@@12NYDarton It is, and my SWR is right down on my five attic dipoles 20m to 10m fed with two random coax lengths but probably 25 feet each. Strange if coax half wave coax does matter how my 14.040 MHz tuned coax works at 10.1 MHz and 18.1 MHz and all five dipoles get out. Shouldn't it be very inefficient at those frequencies? Tx, with 50 Ω RG58 tuned to 14.040 MHz, oscilloscope and 50 Ω dummy load, results below: 14.040 MHz 1 Volt drop. 10.1 MHz 1 Volt drop. 18.1 MHz 1 Volt drop. Shouldn't I get almost nothing out at 10 and 18 if it's tuned to 14.040? Tuned coax theory would say yes I should get very little out. On my VNA it shows an almost flat line from 1.8 MHz to 29 MHz. I can use my coax anywhere within that range. Coax length is nonsense as it gets longer with the jumpers added in. The 'magic' coax length has gone. Why did I bother tuning my coax? To make a video to disprove tuned coax matters. G4GHB.

[@Pioneer936]

@@12NYDarton funny how operators don't understand that swr doesn't blow anything up and that it's the impedance that the radio is putting power into causes the internals to overheat